Lateral spondylolisthesis reduction cage

ABSTRACT

An intervertebral fusion device comprising inferior and superior fusion cage devices that provide an ability to correct spondylolisthesis via in-situ adjustment.

CONTINUING DATA

This application is a continuation of patent application U.S. Ser. No.14/919,863, filed Oct. 22, 2015, entitled “Lateral SpondylolisthesisReduction Cage”, which is a continuation of patent application U.S. Ser.No 14/496,765, filed Sep. 25, 2014, entitled “Lateral SpondylolisthesisReduction Cage”, referred to below as “the '765 application,” each ofwhich is incorporated by reference in its entirety.

The '765 application is a division of patent application U.S. Ser. No.13/163,427, filed Jun. 17, 2011, entitled “Lateral SpondylolisthesisReduction Cage (now U.S. Pat. No. 8,845,733) which claims priority toprovisional application USSN 61/397,716,filed Nov. 30, 2010, entitledLateral Spondylolisthesis Reduction Cage, both of which are incorporatedby reference in their entireties.

The '765 application is a division of patent application U.S. Ser. No13/163,471, filed on Jun. 17, 2011, entitled Instruments and Methods forNon-Parallel Disc Space Preparation (now U.S. Pat. No. 9,282,979) whichclaims priority to provisional application USSN 61/358,220, filed Jun.24, 2010, entitled Instruments and Methods for Non-Parallel Disc SpacePreparation, both of which are incorporated by reference in theirentireties.

The '765 application is a division of patent application U.S. Ser. No13/163,496, filed on Jun. 17, 2011, entitled “Flexible Vertebral BodyShavers”, which claims priority to provisional application USSN61/379,194, filed on Sep. 1, 2010, entitled “Flexible Vertebral BodyShavers”, both of which are incorporated by reference in theirentireties.

The '765 application is a division of patent application U.S. Ser. No13/163,517, filed on Jun. 17, 2011, entitled “Multi-Segment LateralCages adapted to Flex Substantially in the Coronal Plane”, which claimspriority provisional application USSN 61/385,958, filed Sep. 23, 2010,and entitled “Multi-Segment Lateral Cages adapted to Flex Substantiallyin the Coronal Plane”, and also claims priority to provisionalapplication USSN 61/410,177, filed Nov. 4, 2010, and entitled“Multi-Segment Lateral Cages adapted to Flex Substantially in theCoronal Plane”, all of which are incorporated by reference in theirentireties.

The '765 application is a division of patent application U.S. Ser. No13/163,397, filed on Jun. 17, 2011, entitled “Universal Trial forCages”, which claims priority from provisional application USSN61/466,302, filed Mar. 22, 2011, and entitled “Universal Trial forCages”, both of which are incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Lateral interbody fusion procedures are currently indicated for patientswith ≤grade 1 spondylolisthesis. However, correction from the lateralapproach is currently limited to regaining height and lordosis with onlya low degree of spondylolisthesis correction, as the straight orlordotic cage is impacted during insertion to expand the disc space.Significant spondylolisthesis reduction is currently accomplished via aposterior approach with supplemental posterior fixation devices,including facet screws, translaminar screws, pedicle screws and rods, aswell as intraspinous process devices or plates.

Although current lateral cages are characterized by symmetric superiorand inferior geometries, the normal and degenerated discs do not havesuch similar superior and inferior endplate geometries. The lack ofconformity of the cage endplate to the pertinent vertebral body canpromote cage malpositioning during insertion, improper load balancing,increased settling and/or subsidence, as well as device movementfollowing implantation.

Some surgeons using lateral cages attach lateral plating to the cage toachieve enhanced cage securement accompanied by some degree ofbiomechanical stabilization. However, most currently available lateralcages do not provide for plate attachment.

US 2004-0220668 (Eisermann) discloses a method for correctingspondylolisthesis from the lateral approach is provided in which a pairof insertion members are inserted laterally into upper and lowervertebrae, a connecting member is affixed to the insertion members, anda rotating force is applied to the connecting member to encourage theupper and lower vertebrae into a desired position relative to oneanother. In FIGS. 9-11 of Eisermann, in an alternative embodiment, aslidable prosthetic joint can be used to help with the lateral approachfor treating spondylolisthesis. The sliding joint extends generallyalong the longitudinal axis and includes a first slidable component anda second slidable component. The slidable components cooperate to formthe sliding joint which is sized and configured for disposition withinan intervertebral space between adjacent vertebral bodies. The slidingjoint provides movement between the adjacent vertebral bodies tomaintain or restore some of the motion similar to the normalbio-mechanical motion provided by a natural intervertebral disc. Morespecifically, the slidable components are permitted to translaterelative to one another in the axial plane.

US Patent Publication No. 2010-0016968 (Moore) discloses an apparatusand method that allow for the realignment and stabilization of adjacentvertebrae. An implant of this invention both repositions adjacentvertebrae and remains in situ to maintain the new position. The implanthas two halves which are interlocked such that they can slidehorizontally with respect to each other. Movement of the implant halvesand their respective positions are controlled by external set screw andinternal locking block within the implant. The implant includes radialanchors which fit into alignment slots made in the misaligned vertebraby the disclosed method. The set screws are used to advance the halvesof the implant which in turn move the misaligned vertebrae back intocorrect positions. The correct position of the vertebrae is locked inplace through a bolt and a plate.

U.S. Pat. No. 6,342,074 (Simpson) discloses a spinal fusion implant andmethod for maintaining proper lumbar spine curvature and intervertebraldisc spacing where a degenerative disc has been removed. The one-pieceimplant comprises a hollow body having an access passage for insertionof bone graft material into the intervertebral space after the implanthas been affixed to adjacent vertebrae. The implant provides a pair ofscrew-receiving passages that are oppositely inclined relative to acentral plane. In one embodiment, the screw-receiving passages enablethe head of an orthopedic screw to be retained entirely within theaccess passage. A spinal fusion implant embodied in the presentinvention may be inserted anteriorally or laterally. FIG. 4 discloses adevice having fixtures for attaching to a lateral side of a vertebralbody.

U.S. Pat. No. 6,878,167 (Ferree) discloses an osteotomy of a portion ofa vertebral endplate and/or vertebral body allowing for easier insertionof a device that fits tightly into a disc space. It also discloses amechanical device to hold the osteotomized portion of the vertebraagainst the vertebral body after the intradiscal device is placed. Thedevice may be removed after the pieces of vertebra heal and fusetogether. It further discloses a device secured to a side of thevertebral body in FIG. 4C.

SUMMARY OF THE INVENTION

The present invention relates to an intervertebral fusion devicecomprising inferior and superior fusion cages that provide an ability tocorrect spondylolisthesis via lateral insertion and in-situ adjustment.

Therefore, in accordance with the present invention, there is providedan intervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage having an anterior wall, a posterior wall, and        a proximal wall and a distal wall connecting the anterior and        posterior walls, and an upper surface for contacting an upper        vertebral body and a lower surface,    -   b) a lower cage having an anterior wall, a posterior wall, and a        proximal wall and a distal wall connecting the anterior and        posterior walls, and a lower surface for contacting a lower        vertebral body and an upper surface,

-   wherein the lower surface of the upper cage slidingly mates with    upper surface of the lower cage.

Also in accordance with the present invention, there is provided amethod for correcting spondylolisthesis in a patient, comprising thesteps of:

-   -   a) selecting a fusion device comprising an upper cage and a        lower cage,    -   b) fixing the upper cage to an upper vertebral body of the        patient and the lower cage to a lower vertebral body of the        patient, and    -   c) moving the upper cage relative to the lower cage to correct        the spondylolisthesis.

Also in accordance with the present invention, there is provided anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage having an anterior wall, a posterior wall, and        a proximal wall and a distal wall connecting the anterior and        posterior walls, and an upper surface for contacting an upper        vertebral body and a lower surface having a first groove        therein,    -   b) a lower cage having an anterior wall, a posterior wall, and a        proximal wall and a distal wall connecting the anterior and        posterior walls, and a lower surface for contacting a lower        vertebral body and an upper surface having a second groove        therein, and    -   c) a locking plate,

-   wherein the lower surface of the upper cage contacts the upper    surface of the lower cage so that the first and second grooves form    a first throughhole running from the proximal wall to about the    distal wall.

-   wherein the locking plate is disposed in the first throughole.

Also in accordance with the present invention, there is provided anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage having an anterior wall, a posterior wall, and        a proximal wall and a distal wall connecting the anterior and        posterior walls, and an upper surface for contacting an upper        vertebral body and a lower surface,    -   b) a lower cage having an anterior wall, a posterior wall, and a        proximal wall and a distal wall connecting the anterior and        posterior walls, and a lower surface for contacting a lower        vertebral body and an upper surface,

-   wherein the anterior wall is connected to the proximal wall by a    first dual linkage and to the distal wall by a second dual linkage,

-   wherein the posterior wall is connected to the proximal wall by a    third dual linkage and to the distal wall by a fourth dual linkage.

-   wherein the linkages allow the upper plate to pivot relative to the    lower plate in the plane of the proximal wall.

Also in accordance with the present invention, there is provided anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper wall having an upper surface adapted for contacting        an upper vertebral body and an inner surface,    -   b) a lower wall having a lower surface adapted for contacting a        lower vertebral body and an inner surface,    -   c) proximal and distal walls extending between the upper and        lower walls,    -   d) anterior and posterior walls extending between the upper and        lower walls,    -   e) a rack-and-pinion mechanism located between the inner        surfaces of the upper and lower walls

-   wherein the pinion extends substantially from the distal wall to the    proximal wall,

-   wherein the rack extends substantially from the anterior wall to the    posterior wall,

so that rotation of the pinion effects relative movement of the upperand lower walls in the anterior-posterior direction.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a functional spinal unit having grade 1spondylolisthesis characterized by a 20-25% slip.

FIGS. 2a-2b and 3 disclose the implantation of the fusion device of thepresent invention, in which the cages of the device are implanted intothe disc space, brought together, and then locked in place.

FIGS. 4a-4d show various views of the intervertebral fusion device ofthe present invention.

FIGS. 4e-4f show various views of the cages of an intervertebral fusiondevice of the present invention locked with a locking plate.

FIGS. 5a -b disclose a compression-directed inserter of the presentinvention having distal pins, and the insertion of a cage of the presentinvention with this inserter.

FIGS. 5c -d disclose a compression-directed inserter of the presentinvention having distal blades, and the insertion of a cage of thepresent invention with this inserter.

FIGS. 6a-7b disclose how a compression-directed inserter of the presentinvention having nested blades aligns the cages of the present inventionwhen activated.

FIGS. 8a-8d disclose how the cages of one embodiment of the presentinvention are aligned by a rotary spreader, and are locked by aparticular locking plate.

FIGS. 9a-9g disclose various views of a dual linkage embodiment of thepresent invention.

FIGS. 10a-d disclose full and partial views of a rack-and-pinionembodiment of the present invention, some of which are inserted into adisc space.

FIGS. 11a-11e disclose various views of the rack-and-pinion embodimentof the present invention.

FIG. 12 discloses a lateral cage of the present invention with obliquescrewholes.

FIG. 13 discloses an inserter of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a side view of a functional spinal unit having grade 1spondylolisthesis characterized by a 20-25% slip.

In use, the devices of the present invention accomplish improved andcontrolled spondylolisthesis correction with fusion from the lateralapproach. The lateral cage devices of the present invention also providefor intra-operative trialing and selection to enhance conformance of thecage geometry to the vertebral body endplates bounding the targeted discspace. The fusion device of the present invention provides for directattachment of its superior and inferior cages to the lateral aspects ofthe opposing vertebral bodies.

Several devices and methods for correcting spondylolisthesis with fusionfrom the lateral approach are disclosed. All incorporate a superior andinferior fusion cages that are fixedly attached to the correspondingvertebral bodies. The fixed attachment can be accomplished by usingpre-attached plates, or by incorporating internal screws (e.g., theSTALIF approach) and/or lateral keels. Following implantation, thesuperior and inferior cages are aligned in-situ via various activationmeans that are further discussed below, and then locked in place.

The interior, contacting surfaces of the cages that effect intra-deviceattachment contain alignment and securement features that allow forcontrolled intra-operative manipulation of the spine in the sagittalplane following individual fixed attachment of the cages to the superiorand inferior vertebral bodies. These features can include but are notlimited to teeth, barbs, and dovetails.

Both the superior and inferior cages can include features on their outersurfaces that can enhance securement to the vertebral body endplate.These features include fins, barbs, teeth, osteoconductive surfacemorphology (porosity) and coatings (such as HA and TCP). The superiorand inferior cages can also include graft-retention windows and pocketsto facilitate the long-term fusion of the two vertebral bodies of thefunctional spinal unit.

The inner contacting surfaces of the cage can be flat to allow for theincremental lineal adjustment of the relative cage positions.Alternatively, these surfaces can be domed so as to enable the accurateadjustment of the vertebral bodies to a centered position in theflexion/extension plane (i.e., to the center of rotation).

The external geometry of the superior and inferior cages can be flat orlordotic, and can be domed or angled in various plans to enhance theirconformance to the vertebral body endplates and to address spinaldeformity and/or scoliosis.

Following fixed attachment to the vertebral body, the superior andinferior cages may be aligned by several means, including the following:

FIGS. 2a-2b and 3 disclose the implantation of a first embodiment of afusion device of the present invention, in which the cages 501,502 ofthe device are implanted into the disc space, brought together, and thenlocked in place with a locking plate 503. FIGS. 4a-4d show various viewsof the intervertebral fusion device of the present invention. FIGS.4e-4f show various views of the cages of an intervertebral fusion deviceof the present invention locked with a locking plate.

FIG. 2a and FIG. 2b respectively show the relative positions of thefixed cage before and after alignment. In the FIG. 2b position, thecages have properly aligned the vertebral bodies, and thereby correctedthe spondylolisthesis. The superior and inferior cages can also havefeatures that provide or enhance the connection of the cages to thecompressor. These features include recesses, pilot holes and threadslocated on the proximal walls of the two cages (and optionally extendingtherethrough) that receive mating features located on the cage inserter.These features may also assist in the alignment of the cages. Lastly,the upper portion of the proximal wall of the upper cage and the lowerportion of the proximal wall of the lower cage each extend past theanterior and posterior walls of the respective cages, and each has atransverse throughhole. Fixation screws may extend through these holesand into the lateral walls of the corresponding vertebral bodies toprovide the immediate fixation of the cages to these vertebral bodies.Such screw locking features are well known in the art.

As shown in FIGS. 4a,4b and 4 d, the superior and inferior cagestogether preferably form a dovetail joint (or other joint having anexpanding recess) that allows linear anterior-posterior relativemovement of the fixed cages to effect the desired alignment of thevertebral bodies. The contacting surfaces of the superior and inferiorcages may also have matching ratchet teeth, as in FIG. 4d , that provideincremental adjustment of the relative cage positions, and the shortterm inter-cage securement following the compression.

As shown in FIGS. 4e and f , once the superior and inferior cages arealigned together, this desired position may be fixed by attaching asingle locking plate to the proximal ends of each cage. This lockingplate may be attached to the cages by passing screws through the holesin the plate and into the corresponding holes in the lower portion ofthe proximal wall of the upper plate and the upper portion of theproximal wall of the lower plate.

Now referring to FIGS. 4a -4 f, there is provided (claim 1) anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage 1 having an anterior wall 3, a posterior wall        5, and a proximal wall 7 and a distal wall 9 connecting the        anterior and posterior walls, and an upper surface 11 for        contacting an upper vertebral body and a lower surface 13,    -   b) a lower cage 15 having an anterior wall 17 , a posterior wall        19 , and a proximal wall 21 and a distal wall 23 connecting the        anterior and posterior walls, and a lower surface 25 for        contacting a lower vertebral body and an upper surface 27,

-   wherein the lower surface of the upper cage slidingly mates with    upper surface of the lower cage.

In some embodiments, the lower surface of the upper plate and the uppersurface of the lower cage include tongue-and-groove feature. Preferably,the tongue-and-groove feature runs from about the anterior wall to aboutthe posterior wall. Preferably, the tongue-and-groove feature comprisesan expanding recess 29 and more preferably comprises a dovetail 31.

In some embodiments, the lower surface of the upper cage and the uppersurface of the lower cage include a ridge and recess feature 33 thatruns in a proximal-distal direction.

In some embodiments, the proximal wall of the upper cage has a heightHu-p, the anterior wall of the upper cage has a height Hu-a, and whereinthe height of the proximal wall of the upper cage is greater than theheight of the anterior wall of the upper cage .

In some embodiments, the proximal wall of the upper cage has an upperportion 35 having a upper through-hole 37 located above the anteriorwall and adapted for receiving a bone screw.

In some embodiments, the proximal wall of the lower cage has a heightHl-p, the anterior wall of the lower cage has a height Hl-a, and whereinthe height of the proximal wall of the lower cage is greater than theheight of the anterior wall of the lower cage.

In some embodiments, the proximal wall of the lower cage has a lowerportion 39 having a lower through-hole 41 located beneath the anteriorwall and adapted for receiving a bone screw.

In some locking plate embodiments, the proximal wall of the upper cagehas a lower portion 43 having an lower through-hole 45 located beneaththe anterior wall of the upper cage and adapted for receiving a screw.Likewise, the proximal wall of the lower cage has an upper portion 47having an upper through-hole 49 located above the anterior wall of thelower cage and adapted for receiving a bone fastener such as a screw.The device further comprises:

-   -   c) a locking plate 51 having a first and second throughholes 53,        and    -   d) first and second bone fasteners (such as screws) 55,

-   wherein the locking plate is fixed to the proximal wall of the upper    and lower cages by passing the first bone fastener through the first    throughhole of the locking plate and into the lower throughhole of    the upper cage, and by passing the second bone fastener through the    second throughhole of the locking plate and into the upper    throughhole of the lower cage.

In some embodiments that promote fusion, the upper cage furthercomprises a lower surface 13 and a throughole 59 running from the uppersurface to the lower surface. In some embodiments that promote fusion,the lower cage further comprises an upper surface and a througholerunning from the upper surface to the lower surface. Likewise,

the anterior wall further comprises a throughole 61 runningtherethrough. These throughholes are of a size adapted to promote fusion

In some embodiments, the distal end wall of each of the upper and lowercages has a taper 63 for ease of insertion.

In the first embodiment, and now referring to FIGS. 5a -7 b, thealignment means is compression-activated. This preferred embodiment usesa compression instrument to bring the anterior and posterior walls ofthe inferior and superior cages into alignment, and thereby correctspondylolisthesis.

FIGS. 5a-b disclose a compression-directed inserter 65 of the presentinvention having distal pins 67, and the insertion of a cage of thepresent invention with this inserter. FIGS. 5c-d disclose acompression-directed inserter 69 of the present invention having distalblades 71, and the insertion of a cage of the present invention withthis inserter. FIGS. 6a-7b disclose how a compression-directed inserterof the present invention having nested blades 72,73 aligns the cages ofthe present invention when activated.

Now referring to FIG. 5a-d , the compressor instrument may have distalextensions such as blades 71 (FIG. 5c ) or pins 67 (FIG. 5a ) that actto align the anterior and posterior walls of the cages via compression.The blades of FIG. 5c simply push the anterior and posterior walls ofthe cages towards each other, thereby removing any overlap and bringingthe anterior and posterior walls of these cages into vertical alignment.FIGS. 6a-7b disclose the nesting details of the distal portions of thepinned compressor instrument that allow the instrument's distal pins(not shown) to become aligned.

Therefore, in accordance with the present invention, there is provided(claim 16) a method for correcting spondylolisthesis in a patient,comprising the steps of:

-   -   a) selecting a fusion device comprising an upper cage and a        lower cage,    -   b) fixing the upper cage to an upper vertebral body of the        patient and the lower cage to a lower vertebral body of the        patient,    -   c) moving the upper cage relative to the lower cage to correct        the spondylolisthesis.

-   Preferably, the method further comprises the step of: d) locking the    upper cage to the lower cage.

-   In some embodiments, the locking step is accomplished by a locking    plate. In some embodiments, the moving step is accomplished with a    compression-directed inserter.

In some embodiments, the moving step is accomplished with a rotaryspreader.

In a second embodiment, and now referring to FIG. 8a -8 d, the alignmentmeans is rotary spreader-activated. FIGS. 8a-8d disclose how the cagesof one embodiment of the present invention are aligned by a rotaryspreader, and are locked by a particular locking plate. A modifiedspreader or shaver can be inserted into a space formed in the proximalend wall of the unaligned device. Rotating the spreader causes relativeanterior-posterior movement of the upper cage vis-a-vis the lower cageto enable alignment of the cages and thereby intraoperative adjustmentof a spondylosed functional spinal unit (FSU).

Now referring to FIG. 8b , optional locking plates can be employed tofix the device after the spondylolisthesis has been corrected. Theseplates are preferably inserted into bilateral, aligned, longitudinalrecesses that extend across the interface of the aligned cages toprovide inter-cage locking. In some embodiments, these plates are lockedinto place via a snap-lock mechanism, as shown in FIG. 8 d.

In some embodiments, and now referring to FIG. 8a , the upper surface ofthe lower cage and the lower surface of the upper cage may be configuredin matching domes in order to mimic the natural relative arced movementof adjacent vertebral bodies.

Now referring to FIGS. 8a -8 d, there is provided (claim 21) anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage 75 having an anterior wall 77, a posterior wall        79, and a proximal wall 81 and a distal wall 83 connecting the        anterior and posterior walls, and an upper surface 85 for        contacting an upper vertebral body and a lower surface 87 having        a first groove 89 therein,    -   b) a lower cage 91 having an anterior wall 93, a posterior wall        95, and a proximal wall 97 and a distal wall 99 connecting the        anterior and posterior walls, and a lower surface 101 for        contacting a lower vertebral body and an upper surface 103        having a second groove 104 therein, and    -   c) a pair of locking plates 105,

-   wherein the lower surface of the upper cage contacts the upper    surface of the lower cage so that the first and second grooves form    a first throughhole 107 running from the proximal wall to about the    distal wall,

-   wherein the locking plate is disposed in the first throughole.

In some embodiments, the first groove is present upon the lower surfaceof the anterior wall of the upper cage, and the second groove is presentupon the upper surface of the anterior wall of the lower cage. In otherembodiments, the first groove is present upon the lower surface of theposterior wall of the upper cage, and the second groove is present uponthe upper surface of the posterior wall of the lower cage.

In some embodiments, the device of the second embodiment furthercomprises a third groove 109 present upon the lower surface of the uppercage between the anterior and posterior walls, and a fourth groove 111present upon the upper surface of the lower cage between the anteriorand posterior walls, and wherein the lower surface of the upper cagecontacts the upper surface of the lower plate so that the third andfourth grooves form a second throughhole 113 running from the proximalwall to about the distal wall, the second throughhole adapted forinsertion of a spreader therein.

In a third embodiment, and now referring to FIGS. 9a -9 g, theattachment means is linkage activated. FIGS. 9a-9g disclose variousviews of a dual linkage embodiment of the present invention Single- ordouble-linkage can be used to correct spondylolisthesis by moving thiscage from a pre-activated (FIG. 9a ) to a post-activated state. (FIG. 9b) In some linkage embodiments, the anterior and posterior walls of thecages also function as linkage bars, providing for pivoting connectionwith both an upper wall component and a lower wall component to allowfor relative anterior-posterior movement of the upper wall vis-à-vis thelower wall and thereby spondylolisthesis correction.

In some embodiments, and now referring to FIGS. 9c -9 d, the upperportion of the upper wall and the lower portion of the lower wall extendoutwardly, and transverse holes in these portions provide a means to fixthe upper and lower walls to the respective lateral walls of thevertebral bodies.

In some embodiments, and now referring to FIG. 9d , the upper wall andthe lower wall have transverse throughholes that extend into a chamberformed in the interior of the device. These throughholes and thischamber facilitate the fusion of the opposing vertebral bodies throughthe device. Also referring to FIG. 9d , the anterior and posterior wallsmay likewise have transverse throughholes that extend into a chamberformed in the interior of the device, and thereby facilitate the fusionof the opposing vertebral bodies through the device.

Now referring to FIG. 9e -9 g, optional locking plates can be employedto fix the device following spondylolisthesis correction. These platesare preferably inserted into bilateral, aligned, longitudinal recessesthat extend from the upper wall to the lower wall to provide inter-cagelocking. In some embodiments, these plates are locked into place via asnap-lock mechanism, as shown in FIG. 9 e.

Now referring to FIGS. 9a -9 g, there is provided (claim 31) anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage 115 having an anterior wall 117, a posterior        wall 119, and a proximal wall 121 and a distal wall 123        connecting the anterior and posterior walls, and an upper        surface 125 for contacting an upper vertebral body and a lower        surface 127,    -   b) a lower cage 131 having an anterior wall 133, a posterior        wall 135, and a proximal wall 137 and a distal wall 139        connecting the anterior and posterior walls, and a lower surface        141 for contacting a lower vertebral body and an upper surface        143,

-   wherein the anterior wall is connected to the proximal wall by a    first dual linkage 145 and to the distal wall by a second dual    linkage (not shown),

-   wherein the posterior wall is connected to the proximal wall by a    third dual linkage 149 and to the distal wall by a fourth dual    linkage (not shown),

-   wherein the linkages allow the upper plate to pivot relative to the    lower plate in the plane of the proximal wall.

In some aspects of this third embodiment, the proximal wall of the uppercage has a height, the anterior wall of the upper cage has a height, andwherein the height of the proximal wall of the upper cage is greaterthan the height of the anterior wall of the upper cage. In someembodiments thereof, the proximal wall of the upper cage has an upperportion 153 having a upper through-hole 155 located above the anteriorwall and adapted for receiving a bone screw.

In other aspects of this third embodiment, the proximal wall of thelower cage has a height, the anterior wall of the lower cage has aheight, and wherein the height of the proximal wall of the lower cage isgreater than the height of the anterior wall of the lower cage. In someembodiments thereof, the proximal wall of the lower cage has a lowerportion 157 having a lower through-hole 159 located beneath the anteriorwall and adapted for receiving a bone screw.

In some embodiments, the upper cage has a throughole 161 running fromthe upper surface to the lower surface. This throughhole is adapted forpromoting fusion

In a fourth embodiment, the alignment means includes a rack-and-pinion.A pinion located between the upper and lower walls and extendinglaterally can be rotated to move racks extending in theanterior-posterior direction and thereby reduce spondylolisthesis. FIGS.10a-d disclose full and partial views of a rack-and-pinion embodiment ofthe present invention, some of which are inserted into a disc space.FIGS. 11a-11e disclose various views of the rack-and-pinion embodimentof the present invention.

Now referring to FIGS. 10a-11e , there is provided (claim 41) anintervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper wall 171 having an upper surface 173 adapted for        contacting an upper vertebral body and an inner surface 175,    -   b) a lower wall 177 having a lower surface 179 adapted for        contacting a lower vertebral body and an inner surface 181,    -   c) proximal 183 and distal 185 walls extending between the upper        and lower walls,    -   d) anterior 187 and posterior 189 walls extending between the        upper and lower walls,    -   e) a rack-and-pinion mechanism located between the inner        surfaces of the upper and lower walls

-   wherein the pinion 191 extends substantially from the distal wall to    the proximal wall,

-   wherein the rack 193 extends substantially from the anterior wall to    the posterior wall,

-   so that rotation of the pinion effects relative movement of the    upper and lower walls in the anterior-posterior direction.

In some aspects of the fourth embodiment, the length of the device is atleast three times the height of the device.

In some embodiments, the upper and lower walls each have at least onehole 195 therethrough to facilitate fusion through the device. Inothers, the anterior and posterior walls each have at least one hole 197therethrough to facilitate fusion through the device.

In some embodiments, the rack extends from the inner surface of theupper wall. In others, the rack extends from the inner surface of thelower wall.

In some embodiments, the pinion comprises a proximal end 199 having afeature 201 for receiving a rotary tool.

In some embodiments, at least one of the anterior and posterior walls isintegral with at least one of the upper and lower walls.

In some embodiments, at least one of the anterior and posterior walls isremovable.

The embodiments of the present invention may optionally a securementplate that attaches to both the device of the present invention and thevertebral bodies. This securement plate secures the position of thedevice and provides supplemental stabilization.

In general, the devices of the present invention are suited forsubstantially lateral insertion into the disc space. In someembodiments, the cages are inserted through a more anterolateralinsertion angle.

Now referring to FIGS. 4a and 4c , the length L of the device ischaracterized as the distance from the distal wall to the proximal wall.The width W of the device is characterized as the distance from theanterior wall to the posterior wall. The height H of the device ischaracterized as the distance from the lower surface to the uppersurface, excludes the upper and lower portions that extend past theanterior wall, and generally corresponds to the height of the discspace. In general, the length of the lateral devices of the presentinvention are typically at least twice and often three times the widthof the device. In general, the length of the lateral devices of thepresent invention are typically at least twice and often three times theheight of the device. Typically, the width of the device is greater thanthe height of the device.

In some embodiments, as in FIG. 11b , the anterior wall of the cage mayhave a convex curve 203 to mimic the convex shape of the anteriorportion of the disc space

The lateral spondylolisthesis reduction fusion devices of the presentinvention may be produced from a single material or from multiplematerials. These materials include metallics (such as Ti, Ti alloys suchas nitinol, stainless steel, and cobalt-chrome), polymeric materials(including PEEK, PEAK, polypropylene, polyethylene terephthalate (PET),UHMWPE), biologic materials (including allograft, hydroxyapatite, TCPand CaPO₄), and ceramic materials including silicon nitrides, andzirconia-containing ceramics. The plate, fasteners, or lockingmechanisms can be produced from metallics or polymers for enhancedurability.

Additionally, modified versions of this concept can be designed tocorrect spondylolisthesis with superior and inferior cages that areinserted from the anterior, anterior-lateral or posterior approaches.

The cages of the present invention are preferably inserted either from aright lateral or left lateral approach.

Following standard access and disc preparation procedures, the superiorand inferior cages are inserted and affixed to the opposed vertebralbodies with screws or bone fasteners. Spondylolisthesis correction isthen performed with the disclosed compressor or with a rotary tool.Optionally, locking members are then applied to the superior andinferior cages to fix the orientation of the segments.

Also in accordance with the present invention, there is provided amethod of implanting an intervertebral device between opposed vertebralbodies, comprising the steps of:

-   -   i) selecting an intervertebral device comprising:        -   a. an upper half component having an anterior wall, a            posterior wall, and two side walls connecting the anterior            wall and posterior wall;        -   b. a lower half component having an anterior wall, a            posterior wall, and two side walls connecting the anterior            wall and posterior wall;    -   ii) inserting the device between opposed vertebral bodies,        whereby the anterior walls are not aligned,    -   iii) moving (preferably by pivoting) one of the components with        respect to the other component so that the anterior walls are        substantially aligned, and    -   iv) fixing the device to the opposed vertebral bodies.

In some embodiments of the present invention, the fusion device isangled to provide either lordosis or kyphosis. In embodiments in whichlordosis is desired, the height of the anterior wall exceeds the heightof the posterior wall. An example of such a lordotic implant is shown inFIG. 4c . In embodiments in which kyphosis is desired, the height of theanterior wall is less than the height of the posterior wall.

It is believed by the present inventors that the devices disclosedherein appear to be the first intervertebral devices having a flangethat connects to a side of a vertebral body. Therefore, in accordancewith the present invention, there is provided a method of inserting afusion device between opposed vertebral bodies, comprising the steps of:

-   -   a) selecting an intervertebral device having an anterior wall, a        posterior wall and a pair of side walls connecting the anterior        and posterior walls, wherein at least one of the side walls has        a flange axially extending beyond the anterior wall and the        posterior wall, wherein the flange has a throughhole,    -   b) inserting the device between the opposed vertebral bodies,        and    -   c) inserting a fixation device through the throughhole to fix        the device to a side of one of the opposed vertebral bodies.

Although the cages of the present invention are disclosed as havingflanges that extend beyond the disc space for attachment to the sides ofthe opposed vertebral bodies, it is also contemplated that the cages ofthe present invention may be attached to the opposed vertebral bodiesvia zero profile throughholes. These zero profile throughholes areprovided both a) at the upper edge of the proximal side wall of theupper half component and b) at the lower edge of the proximal side wallof the lower half component.

Therefore, in accordance with the present invention, there is providedan intervertebral fusion device for correcting spondylolisthesis in apatient, comprising:

-   -   a) an upper cage having an anterior wall, a posterior wall, and        a proximal wall and a distal wall connecting the anterior and        posterior walls, and a throughole present at the upper edge of        the proximal wall for receiving a bone fixation device,    -   b) a lower cage having an anterior wall, a posterior wall, and a        proximal wall and a distal wall connecting the anterior and        posterior walls, and a lower surface for contacting a lower        vertebral body and an upper surface, and a throughole present at        the lower edge of the proximal wall for receiving a bone        fixation device,

-   wherein the lower surface of the upper cage slidingly mates with    upper surface of the lower cage.

Although the above description discloses how to make and use implantabledevices to correct spondylolisthesis, it is within the scope of theinvention to use these devices as instruments to correct retrolisthesisas well. Therefore, in accordance with the present invention, there isprovided a method for correcting spondylolisthesis in a patient,comprising the steps of:

-   -   a) selecting an instrument comprising an upper cage and a lower        cage, wherein each cage is attached to a handle    -   b) attaching the upper cage to an upper vertebral body of the        patient and the lower cage to a lower vertebral body of the        patient (preferably with caspar pins),    -   c) moving the upper cage relative to the lower cage to correct        the spondylolisthesis (preferably with a distractor that engages        the caspar pins), and    -   d) removing the instrument from the patient.

Although the above description discloses how to make and use devices inthe context of correcting spondylolisthesis, it is within the scope ofthe invention to use similar devices to correct retrolisthesis as well.

FIG. 12 discloses a lateral cage of the present invention with obliquescrewholes 301.

FIG. 13 discloses an inserter 303 of the present invention. FIG. 13 is atop view of a second type of spondylolisthesis reduction tool thatcomprises a proximal handle portion 305 and two vertebral body engagingbeams 307. On the distal end of the beams are bone engaging features 309for the respective superior and inferior vertebral bodies. At theproximal end of the beams the inferior beam is fixed within the handleand the superior is attached with a pivot so that its distal end canmove posterior and anterior with respect to the lower. Conversely, thelower beam could also be affixed in a pivoting fashion so that bothbeams move as in a scissor fashion. This intended motion corresponds toa posterior transverse plane motion of the superior vertebral body inorder to reduce the spondylolisthesis. By slightly rotating the handleor tilting the tool prior to engagement, a saggital plane component isintroduced to the reduction motion (it may be beneficial to increase theheight of one body over the other as you move that body posteriorly).

The cross section of the beams are sufficiently wide in theanterior-posterior direction making them resistant to bending in thetransverse plane. The mechanism within the handle is to pivot the beams.This can be done with a ratchet and pawl linkage which moves the topbeam one click with each squeeze, or a sliding collar that advancesdistally along the beams to bring them in line with each other, or awedge/roller that advances along the edge of the superior beam or a postand angled slot mechanism that aligns the two beams, or with a gearedscissor mechanism such that the full motion of the handle corresponds toa small angular change of the beams. The controlled motion of the beamsrelative to each other is advantageous as the operating surgeongenerally has a pre-determined amount of reduction in mind for thesurgery. This amount can be determined via radiograph orinter-operatively. For example if a total of 6 mm of reduction isdesired, the handle can be ratcheted 1 mm at a time until the value of 6mm is reached.

-   Therefore, there is provided a spondylolisthesis reduction tool    comprising:    -   a) a proximal handle portion, and    -   b) first and second vertebral body-engaging beams having a        longitudinal axis, a proximal end portion and a distal end        portion, the distal end portion of each beam forming bone        engaging features,-   wherein the proximal end portion of the first beams is fixedly    attached to the handle portion, and-   wherein the proximal end portion of the second beam is pivotally    attached to the handle portion-   so that the second beam can move transversely with respect to the    longitudinal axis of the first beam.-   Preferably, the handle portion comprises a trigger 311 adapted to    pivotally move the second beam.

We claim:
 1. A method of installing an intervertebral fusion device,wherein the device comprises: a) an upper endplate having an anteriorwall, a posterior wall, an upper surface for contacting an uppervertebral body of a patient, teeth extending from the upper surface forenhancing securement, a lower surface, and a throughhole running fromthe upper surface to the lower surface and adapted for promoting fusion,b) a lower endplate having an anterior wall, a posterior wall, a lowersurface for contacting a lower vertebral body of the patient, teethextending from the lower surface for enhancing securement, an uppersurface, and a throughhole running from the lower surface to the uppersurface and adapted for promoting fusion, c) a first core componenthaving an upper endportion engaged with the upper endplate and a lowerendportion engaged with the lower endplate, and d) a second corecomponent having an upper endportion engaged with the upper endplate anda lower endportion engaged with the lower endplate, wherein the devicehas a collapsed configuration and an expanded configuration, wherein theupper endplate does not contact the lower endplate in the expandedconfiguration, wherein each of the upper endplate, the upper endportionof the first core, and the upper end portion of the second core movesaway from the lower surface of the lower endplate during expansion fromthe collapsed configuration to the expanded configuration, wherein themethod comprises: inserting the device into a disc space so that theanterior wall of the upper endplate faces anteriorly relative to thepatient and the posterior wall of the upper endplate faces posteriorlyrelative to the patient, and expanding the inserted device from thecollapsed configuration to the expanded configuration, wherein each ofthe anterior and posterior walls of the upper endplate moves posteriorlyduring expansion from the collapsed configuration to the expandedconfiguration.
 2. The method of claim 1, wherein the first corecomponent is unitary and the second core component is unitary.
 3. Themethod of claim 1, further comprising e) at least one screw extendingthrough an opening formed in a proximal end of the device andsubstantially parallel to a longitudinal axis of the upper endplate. 4.The method of claim 1, wherein the upper surface of the upper endplateand the lower surface of the lower endplate are domed.
 5. The method ofclaim 1, wherein the upper and lower endplates are tapered for ease ofinsertion into the disc space.
 6. The method of claim 1, wherein theupper and lower endplates are formed from titanium or a titanium alloy.7. The method of claim 1, wherein at least one of the first corecomponent and the second core component is disposed on a proximalsurface of the upper endplate or a proximal surface of the lowerendplate.